In the making of paper a suspension of fibers, size, and water is poured as a wide band onto a continuously moving mesh also known as a Fourdrinier wire. This mesh is normally made of bronze and is extremely fine, in fact so fine that light can scarcely pass through it, so that the solid phase of the suspension will remain on the mesh while the liquid phase--the water--will drop through it.
In most systems the mesh is supported at the upstream end, the so-called wet end of the process, by means of transversely extending bars, also known as foils, having sharp edges directed forwardly into the direction of travel of the screen. These bars serve for dewatering of the paper being formed on the screen in its preliminary stages of production. To this end their leading edges must be very sharp for clean stripping of the moisture from the underside of the mesh. These upper surfaces of the bars are normally made of extremely hard material, such as a silicate, as described in my U.S. Pat. No. 4,047,993 and in my copending application Ser. No. 807,330 filed June 16, 1977 (now U.S. Pat. No. 4,164,442).
Even though the upper surface of these bars which are in contact with the normally bronze mesh are of such extremely hard material, it is nonetheless necessary occasionally to withdraw and either replace or clean the bars. For this purpose it is known to mount the bars on transversely extending guides so that the bars can be pulled transversely out from underneath the mesh. During this operation the entire machine is usually shut down so as to be able to lift the mesh off the bar or bars being replaced. It is normally considered unthinkable to displace the bars with their sharp edges out from underneath the mesh while the machine is in operation because this could easily damage the mesh which as a result of its fineness, extreme length in the neighborhood of several hundred meters, and material, is an extremely expensive item that can cost several thousand dollars. Thus the servicing of these dewatering and support bars represents a considerable bottleneck in the papermaking process.
Other prior-art systems are seen in Austrian Pat. Nos. 302,800 and 311,783 as well as in German Pat. No. 949,979 and in U.S. Pat. No. 3,576,716.